Fast base station switching method and system, and hierarchical zone-based fast handoff approach

ABSTRACT

A method of performing fast base station switching for hand off is provided that involves the use of a tunnel from a serving base station to a target base station. During a hand off, packets are forwarded by the serving base station to the target base station using the tunnel. A hierarchical hand off method is also provided that uses a diversity hand off method for a hand off between base stations of different zones, and uses a non-diversity handoff, such as the fast base station switching method, for a hand off between base stations in the same zone.

FIELD OF THE INVENTION

The invention relates to handoff in wireless networks.

BACKGROUND OF THE INVENTION

The latest Broadband wireless data network technology development,including WiFi (802.11), WiMAX (802.16e) and DSRC (802.11p) technology,is progressing to large scale and full mobility. To support fullmobility, various handoff (HO) procedures have been defined. Primarily,three handoff technologies are being developed:

1) Soft handoff (SOHO): SOHO is a make-before-break approach. In SOHO,an ASN (Access Service Network) anchor point device multicasts the samedata flows to both a serving base station (base station) and allpotential target base station. The mobile station (mobile station) has aselector to decide which target base station it is going to talk to whenit moves from the serving base station to the next base station. Anadvantage of SOHO is that there will be no data packet loss duringhandoff because the same packets have been sent to the new target basestation before the mobile station attaches to that new base station. Adisadvantage for SOHO is that additional system resources (buffers, CPU,bandwidth, and air spectrum) are required to support the multicast dataflows.2) Hard handoff (HDHO): HDHO is a break-before-make approach. In thiscase, a mobile station just simply drops a connection with the currentserving base station, and re-establishes a new connection with a newtarget base station. During handoff, all the packets that werepreviously sent to the serving base station are lost, and the serviceflow has to be re-created using higher layer protocols. For example,where TCP is employed, the TCP layer would drop the original session andrebuild a new session. An advantage of HDHO is that it is simple anddoes not cost much in terms of system resources. A disadvantage is thatthe data path interruption may last up to 100+ ms to seconds. This leadsto packet loss that can dramatically impact application performance.3) Fast Base Station Selection: With this approach, fast selectionbetween a serving base station and a target base station is performed tosupport handoff and reduce the packet loss. The faster the selectionspeed is, the less packet loss is suffered, and the closer theperformance is to that of SOHO. The slower the switching performed withfast base station selection, the closer the performance is to that ofHDHO. Fast base station selection is also referred to in section 3.7.6of a 802.16-2005 document as follows:

-   -   The mobile station (mobile station) is only        transmitting/receiving data to/from one of active base station        (anchor base station) at any give time. The anchor base station        can change from frame to frame depending on the base station        (base station) selection schema.

SUMMARY OF THE INVENTION

According to one broad aspect, the invention provides a method ofperforming fast base station switching of a mobile station'scommunications from a first base station to a second base stationcomprising: a first base station acting as a serving base stationreceiving packets from a data source destined for the mobile station;the first base station transmitting packets to the mobile station; toimplement the fast base station switch to the second base station, thefirst base station forwarding to the second base station all packetsthat have not been transmitted to the mobile station or that have notbeen acknowledged by the mobile station; the second base stationreceiving the packets from the first base station; the second basestation transmitting packets received from the first base station to themobile station; later, the second base station receiving packets fromthe data source destined for the mobile station such that the secondbase station acts as a serving base station.

In some embodiments, the method further comprises: establishing a tunnelbetween the first base station and the second base station forforwarding packets between the first base station and the second basestation.

In some embodiments, the method further comprises: for a handoff zonecomprising a plurality of base stations and a data source, establishinga plurality of tunnels between pairs of the base stations such that theswitch from a first base station to a second base station can beperformed for any of the pairs of base stations.

In some embodiments, the method further comprises: at the first basestation: a) during non-handoff operation, receiving the packets on aningress port and queuing them in an ingress queue; b) during non-handoffoperation, de-queuing packets from the ingress queue and transmittingthem over an air interface; c) during handoff, de-queuing packets fromthe queue and re-queuing them in an egress queue; d) during handoff,de-queuing packets from the egress queue and sending them to the secondbase station on an egress handoff port; at the second base station: d)during handoff, receiving the packets on an ingress handoff port andqueuing them in an ingress queue; f) during handoff, de-queuing packetsfrom the ingress queue and transmitting them over an air interface.

According to another broad aspect, the invention provides a methodcomprising: defining a plurality of non-diversity handoff zones, eachnon-diversity handoff zone comprising a respective plurality ofnon-diversity-enabled base stations; to perform a handoff between afirst base station and a second base station of said base stations:performing a non-diversity handoff to complete the handoff if the firstbase station and the second base station are in the same non-diversityhandoff zone; performing a diversity handoff to complete the handoff ifthe first base station and the second base station are in differentnon-diversity handoff zones.

In some embodiments, performing a non-diversity handoff comprisesperforming fast base station selection.

In some embodiments, performing a non-diversity handoff comprisesperforming fast base station switching.

In some embodiments, performing fast base station switching comprises: afirst base station acting as a serving base station receiving packetsfrom a data source destined for the mobile station; the first basestation transmitting packets to the mobile station; to implement thefast base station switch to the second base station, the first basestation forwarding to the second base station all packets that have notbeen transmitted to the mobile station or that have not beenacknowledged by the mobile station; the second base station receivingthe packets from the first base station; the second base stationtransmitting packets received from the first base station to the mobilestation; later, the second base station receiving packets from the datasource destined for the mobile station such that the second base stationacts as a serving base station.

In some embodiments, the method further comprises: establishing a tunnelbetween the first base station and the second base station forforwarding packets between the first base station and the second basestation.

In some embodiments, the method further comprises: at the first basestation: a) during non-handoff operation, receiving the packets on aningress port and queuing them in an ingress queue; b) during non-handoffoperation, de-queuing packets from the ingress queue and transmittingthem over an air interface; c) during handoff, de-queuing packets fromthe queue and re-queuing them in an egress queue; d) during handoff,de-queuing packets from the egress queue and sending them to the secondbase station on an egress handoff port; at the second base station: d)during handoff, receiving the packets on an ingress handoff port andqueuing them in an ingress queue; f) during handoff, de-queuing packetsfrom the ingress queue and transmitting them over an air interface.

In some embodiments, the method further comprises: defining a pluralityof virtual base stations each comprising a relay and a base stationserved by the relay; wherein for the purpose of non-diversity handoffzones, each virtual base station is treated as a non-diversity-enabledbase station.

In some embodiments, the method further comprises: providing service toat least one mobile station with a mobile relay, the mobile relay andserved mobile station comprising a mobile relay and mobile station pair;to perform a handoff of a mobile relay and mobile station pair between afirst base station and a second base station of said base stations:performing a non-diversity handoff to complete the handoff if the firstbase station and the second base station are in the same non-diversityhandoff zone; performing a diversity handoff to complete the handoff ifthe first base station and the second base station are in differentnon-diversity handoff zones.

According to another broad aspect, the invention provides a systemcomprising: a plurality of base stations organized into non-diversityhandoff zones; an inter-zone handoff controller; the system beingadapted to perform handoffs between a first of the base stations and asecond of the base stations by: performing a non-diversity handoff tocomplete the handoff if the first base station and the second basestation are in the same non-diversity handoff zone; performing adiversity handoff under control of the inter-zone handoff controller tocomplete the handoff if the first base station and the second basestation are in different non-diversity handoff zones.

In some embodiments, the system is adapted to perform a non-diversityhandoff by performing fast base station selection.

In some embodiments, the system is adapted to perform a non-diversityhandoff by performing fast base station switching.

In some embodiments, the system is adapted to perform fast base stationswitching by: a first base station acting as a serving base stationreceiving packets from a data source destined for the mobile station;the first base station transmitting packets to the mobile station; toimplement the fast base station switch to the second base station, thefirst base station forwarding to the second base station all packetsthat have not been transmitted to the mobile station or that have notbeen acknowledged by the mobile station; the second base stationreceiving the packets from the first base station; the second basestation transmitting packets received from the first base station to themobile station; later, the second base station receiving packets fromthe data source destined for the mobile station such that the secondbase station acts as a serving base station.

In some embodiments, the system further comprises a network hierarchicalhandoff control architecture comprising said master handoff controllerat inter-zone level, zone-handoff-controllers at intra-zone level andhandoff-agents at each base station.

In some embodiments, the system is adapted to establishing a tunnelbetween the first base station and the second base station forforwarding packets between the first base station and the second basestation.

In some embodiments, the first base station is adapted to: a) duringnon-handoff operation, receiving the packets on an ingress port andqueuing them in an ingress queue; b) during non-handoff operation,de-queuing packets from the ingress queue and transmitting them over anair interface; c) during handoff, de-queuing packets from the ingressqueue and re-queuing them in an egress queue; d) during handoff,de-queuing packets from the egress queue and sending them to the secondbase station on an egress handoff port; the second base station isadapted to: d) during handoff, receiving the packets on an ingresshandoff port and queuing them in an ingress queue; f) during handoff,de-queuing packets from the ingress queue and transmitting them over anair interface.

According to another broad aspect, the invention provides a base stationcomprising: at least one input port for receiving packets destined formobile stations; an output port for outputting packets on a tunneltowards another base station; physical layer hardware; a packetdispatcher adapted to transmit received packets for a given mobilestation to the given mobile station via the physical layer hardwarewhile the given mobile station is attached to the base station, and tosend the packets towards the output port during a fast base stationswitch handoff to the another base station.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described withreference to the attached drawings in which:

FIG. 1 is a flowchart of a method of performing fast base stationswitching in accordance with an embodiment of the invention;

FIG. 2 is a block diagram of a network adapted to perform fast basestation switching in accordance with an embodiment of the invention;

FIG. 3 is a detailed schematic diagram of a pair of base stationsperforming a fast base station switching;

FIG. 4 is a flowchart of a method of performing hierarchical zone-basedhandoff;

FIG. 5 is a block diagram of a system that performs hierarchicalzone-based handoff;

FIG. 6 is another block diagram of a system that performs hierarchicalzone-based handoff;

FIGS. 7A and 7B depict two examples of handoff in networks that employrelays in the path between base stations and mobile stations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the invention provides a method of performing fast basestation switching. Referring to FIG. 1, the method involves performingthe following steps:

Step 1-1: a first base station acting as a serving base station receivespackets from a data source destined for the mobile station. In someimplementations, the packets may be segmented and re-assembled;

Step 1-2: the first base station transmits queued packets to the mobilestation;

Step 1-3: the first base station receives an indication (that might betriggered from the data source or from the mobile station for example),or otherwise making a determination that a fast base station switch to asecond base station should be performed;

Step 1-4: to implement the fast base station switch to the second basestation, the first base station forwards to the second base station allpackets received from the data source that have not been transmitted tothe mobile station, or that have been transmitted but not acknowledgedby the mobile station; for example, this might involve transferring boththe packets that have not been acknowledged, and packets that have notyet been transmitted from an ingress queue (e.g., via an ARQ (automaticrepeat request) dispatcher) to an egress queue for transmission on ahandoff tunnel;Step 1-5: the second base station receives the packets from the firstbase station and queuing them for transmission to the mobile station;Step 1-6: the second base station transmits packets received from thefirst base station to the mobile station;Step 1-7: later, the mobile station notifies the data source of thesuccessful handoff operation, and the data source stops sending packetsto the first base station, and redirects the packets to the second basestation. The second base station then receives packets from the datasource destined for the mobile station such that the second base stationacts as a serving base station.

In the above-described method, the data source can be an anchor pointfor communication with the base stations and possibly other basestations. In some embodiments, context information is forwarded from thefirst base station to the second base station before starting to forwardpackets between the two base stations.

In some embodiments, the method further involves establishing a tunnelfrom the first base station to the second base station to carry theforwarded traffic. In some embodiments this tunnel is pre-configuredsuch that any handoff from the first base station to the second basestation is executed using the pre-configured tunnel. In otherembodiments, the tunnel is configured on demand, for example using theMPLS (multi protocol label switching) RSVP protocol. The tunnels can beimplemented using any suitable technology, typically dependant on thetechnology of the zone gateways. Specific examples include IP-in-IP,Mac-in-Mac, MPLS label stack, resilient packet ring (RPR), and opticalchannels.

In some embodiments, the first part of the method described, namely theforwarding of packets from the first base station to the second basestation via fast base station switching, is implemented without anyinvolvement of network-dependent data plane forwarding intelligence,other than possibly as an element in the path of elements participatingin the forwarding of packets. The control plane for handoff operation(e.g., target base station selection, data path redirection, etc.) maystill involve collaboration between the base stations and the datasource.

The method is referred to herein as fast base station switching becausepackets are forwarded (i.e. effectively “switched”) to a selected basestation without the network performing a switch between base stations,at least not until the end of the method when the packet flow isre-directed.

Referring now to FIG. 2, shown is a block diagram of a network that canbe used to implement the fast base station switching method describedabove. The network consists of a plurality of base stations 202,204,206(only three shown, but more generally any number can be included)connected through a network 208 to a zone gateway 200. The base stations202,204,206 have coverage areas 210,212,214 respectively. An overlapbetween coverage areas 210 and 212 is indicated at 216 and an overlapbetween coverage areas 212 and 214 is indicated at 218. The zone gateway200 sends and receives traffic as indicated at 224 on behalf of the basestations within the zone, namely base stations 202,204,206, and morespecifically on behalf of mobile stations within the coverage areasserved by these base stations.

An example of fast base station switching will now be described in thecontext of the network of FIG. 2. Initially, assume there is a mobilestation within coverage area 210 being served by base station 202. Inthis case, traffic is being forwarded bi-directionally between the zonegateway 200 and the base station 202 on behalf of the mobile station.When the mobile station moves within the overlap 216 between thecoverage areas 210,212 of base stations 202,204, eventually a decisionis made to start serving the mobile station from base station 204 ratherthan base station 202. To achieve this, once this decision is made, basestation 202 forwards the mobile station's traffic consisting of trafficthat it has received for the mobile station but not yet transmitted (ornot yet acknowledged) to the mobile station, and any further trafficthat it receives for the mobile station, on a tunnel 220 establishedthrough network 208 between base station 202 and base station 204. Asimilar tunnel is indicated at 222 to enable forwarding of traffic frombase station 204 to base station 206. Tunnels 220,222 can either bepre-configured, or set up upon demand. The base station 204 receives thetraffic for the mobile station over the tunnel 220 and then transmits itover the air interface to the mobile station within coverage area 212.At some later time, for example after traffic has stabilized and themobile station is no longer in the overlap area 216, the zone gateway200 will be signalled to forward packets directly to base station 204for the mobile station.

A specific implementation suitable for use in an ARQ-enabled WiMAXnetwork will now be described with reference to FIG. 3. When mobility ofa mobile station occurs, a mobile station sends/receives handoff-requestand/or handoff-confirm to/from serving base station. These messages maytrigger FBSS handoff tunnel creation between serving base station andthe chosen target base station (if it is not created before.)

Referring now to FIG. 3, shown is a specific implementation of the fastbase station switching approach described above with reference to FIG.2. Shown in the detailed example is a zone gateway 50 and two basestations 52,54. There may be a network 51 between the zone gateway 50and the base stations 52,54. At the instant depicted, base station 52 isa serving base station while base station 54 is a target base station.The serving base station 52 receives packets for a mobile station (notshown) through ingress port 56 from where they are queued into a queue60. An ARQ dispatcher 62 takes care of downlink packet transmission tothe physical layer, in the illustrated example this being an 802.16 OFDMPHY layer. The ARQ dispatcher 62 de-queues packets from the queue 60.Assuming that the mobile station is still within the coverage area ofthe serving base station 52 and that no handoff is to be executed, thepackets are then forwarded on to the physical layer 64 for transmissionover the air interface. In the illustrated example, the physical layeris an 802.16 physical layer, but more generally any appropriate physicallayer technology can be employed. On the other hand, if the mobilestation has moved so as to be within the coverage area of the targetbase station 54, and it indicates the desire to attach to target basestation 54, then packets are to be forwarded to the target base station54 on behalf of the mobile station. To achieve this, the ARQ dispatcher62 switches over the packets to an egress queue 66. Furthermore, packetsthat come from a mobile station via the physical layer 64 are alsoqueued in the egress queue 66.

The manner in which queuing is performed is implementation specific.There may be separate egress queues for downlink traffic that is beingre-routed to a target base station and for uplink traffic originatedfrom a mobile station. In some embodiments, there is separate queue orqueues for each mobile station being served by the base station.

There is an ARQ distributor 68 that de-queues packets from the egressqueue 66. In the specific example illustrated, the ARQ distributorreceives 802.16 MAC PDUs from the OFDM PHY and delivers them to theuplink or handoff tunnel. Packets that originated from the ARQdispatcher are forwarded on to handoff tunnel port 72, while packetsthat originated from the physical layer 64 are forwarded on to egressport 70. Packets from egress port 70 are then forwarded in an uplinkdirection through the network to their destination. On the other hand,packets forwarded by the handoff tunnel port 72 are transmitted over atunnel 74 to the target base station 54. Tunnel 74 can either beestablished on demand when it becomes necessary to perform the handoff,or the tunnel can be pre-configured between the serving base station 52and the target base station 54. In the illustrated example, the tunnel74 is shown passing through network 51 and not the zone gateway 50. Insome instances, the tunnel 74 may be established through the zonegateway 50.

In some implementations, to implement the packet forwarding, the servingbase station control plane commands the ARQ dispatcher to loop-backsequenced MAC PDU from an ingress ARQ-enabled buffer to an egressARQ-enabled buffer. The original outgoing packets now become incomingpackets to be tunnelled to target base station.

The target base station 54 receives downlink packets from the zonegateway 50 at ingress port 80 and they are queued in ingress queue 84.Furthermore, during a handoff the target base station also receivespackets via the tunnel 74 at the handoff tunnel port 82 and they arealso queued in ingress queue 84. Again, the manner in which queuing isperformed is implementation specific. There may be separate ingressqueues for non-handoff traffic that is being received from the zonegateway and for traffic re-routed from another base station. In someembodiments there is a separate queue or queues for each mobile station.The ARQ dispatcher 86 de-queues packets from the ingress queue 84 andtransmits them over the physical layer 88. Furthermore, uplink packetsreceived over the air interface by the physical layer 88 are queued inegress queue 90. They are de-queued by the ARQ distributor 92 andtransmitted over egress port 94.

In some embodiments, where each packet is segmented into many blockswith associated sequence numbers (the sequence number is used forreliable transmission/re-transmission in which each receipt of eachblock has to be acknowledged), the ARQ distributor at serving basestation 52 co-ordinates the unacknowledged sequence numbers of outgoingMAC PDUs with the ARQ dispatcher at the target base station 54 from thereceived MAC PDU. The unacknowledged MAC PDU will be re-transmitted atthe target base station 54 after the mobile station attaches to it.

After a connection is well established between the target base stationand the mobile station, the target base station will send a notificationto the zone gateway. At that point, the zone gateway begins forwardingthe same service flow directly to the target base station, and stopssending packets to original serving base station.

When the FBSS handoff tunnel is empty, both the serving base station andthe target base station restore their normal operations. In someembodiments, this involves releasing un-needed system resources untilthe next handoff happens.

With the example of FIG. 3, the functionality of serving base station 52is only shown for the base station in its capacity as a serving basestation; similarly the functionality of target base station 54 is onlyshown in respect of its capacity as a target base station. Moregenerally, typically a given base station would be able tosimultaneously function as both a target base station for one or moremobile stations and a serving base station for one or more differentmobile stations in which case the combined functionality of both basestations 52,54 would be implemented in each base station.

Another embodiment of the invention provides a single base stationadapted to implement fast base station switching. Specific examples arethe base stations 52,54 of FIG. 3. In another specific example, a basestation adapted to implement fast base station switching has at leastone input port for receiving packets destined for mobile stations; anoutput port for outputting packets on a tunnel towards another basestation; physical layer hardware; and a packet dispatcher adapted totransmit received packets for a given mobile station to the given mobilestation via the physical layer hardware while the given mobile stationis attached to the base station, and to send the packets towards theoutput port during a fast base station switch handoff to the anotherbase station.

In another embodiment of the invention, a hierarchical zone-basedhandoff approach is employed that combines inter-zone soft handoff andintra-zone FBSS. Referring to the flowchart of FIG. 4, the method beginsat step 4-1 with defining a plurality of fast base station switchingzones, each fast base station switching zone comprising a respectiveplurality of FBSS-enabled base stations. An FBSS-enabled base station isone that can participate in the fast base station switching handoffdescribed above with reference to any one of FIGS. 1 to 3. If it isdetermined that it is necessary to perform a handoff between a firstbase station and a second base station, (yes path, step 4-2) then fastbase station switching is performed to complete the handoff at step 4-3.If it is determined that it is necessary to perform handoff between afirst base station and a second base station, and the first base stationand the second base station are in different fast base station switchingzones, (yes path, step 4-4), then soft handoff is performed to completethe handoff.

FIG. 5 is a block diagram of a specific network adapted to implement themethod described above. Shown is a inter-zone handoff controller 10connected to a multicast network 12 that is in turn connected to aplurality of zone gateways 20,21,22. Each zone gateway 20,21,22 serves arespective coverage area referred to as an FBSS zone 14,16,18. Each ofthese zones includes a respective plurality of FBSS-enabled basestations. For example, FBSS zone 14 is shown to include base stations22,24. Also shown is a data source 11. The inter-zone handoff controller10 implements control over handoffs between zones. Actual traffic doesnot pass through the inter-zone handoff controller 10 in the illustratedexample, but in other implementations, the inter-zone handoff controller10 may also function as an inter-zone gateway in which case it alsoprocesses traffic.

More generally, any number of zone gateways might be implemented, andfor each zone gateway, any number of base stations might be implemented.Multicast network 12 is simply any network that will enable theinter-zone gateway 10 to transmit packets to multiple of the zonegateways during an inter-zone handoff.

In operation, when a handoff between two base stations served by a givenzone gateway, for example base stations 22,24 served by zone gateway 20,is to be executed, a fast base station switch handoff is executed withinthat zone.

On the other hand, if a handoff is to take place between two basestations and two FBSS zones, for example between base station 24 of FBSSzone 14, and base station 25 of FBSS zone 16, then a soft handoff isemployed. This involves the inter-zone gateway 10 forwarding datapackets through the multicast network 12 to both zone gateway 20 andzone gateway 21 for forwarding on to respective base stations 24,25. Inthis case, both base stations 24,25 transmit the packets over the airinterface, and the mobile station can receive both of these and eitherselect between them or perform diversity combining. More generally,methods of performing soft handoff are well understood, and for the casewhere soft handoff is to be performed between the base stations of twodifferent FBSS zones, any appropriate soft handoff mechanism can beexecuted.

Detailed examples of how fast base station switching might beimplemented have been described above with reference to FIGS. 1 to 3.For the purpose of the embodiment of FIG. 5, a hierarchical approach hasbeen described that employs soft handoff on a higher hierarchical level,and employs FBSS on a lower level, within zones. More generally, inanother embodiment of the invention, a hierarchical approach is employedin which a diversity handoff approach is used on a higher hierarchicallevel to handle handoffs between zones while a non-diversity handoffapproach is used within individual zones referred to as non-diversityhandoff zones. With a diversity handoff approach, multiple copies of asignal are available to a receiver and the receiver can either selectbetween them or combine them. Soft handoff is a specific example ofdiversity handoff. With a non-diversity handoff approach, there is onlyone copy of a signal available to a receiver. Fast base stationselection and fast base station switching are two specific examples ofnon-diversity-based handoff.

A specific example of the network of FIG. 5 is shown in FIG. 6. In thiscase, the multicast network 12 consists of a resilient packet ring 38serving as a global backbone that interconnects the inter-zone handoffcontroller 10 and the zone gateways 20,21,22. This allows for azone-based handoff procedure built upon a hierarchical ring-tree networktopology. The top level of this architecture is an handoff-enabledRPR-like topology, and it is controlled by a master handoff controlfunction to conduct inter-zone data traffic anchor pointing. The masterhandoff control function can be implemented as part of the inter-zonehandoff controller or it might be a specific functional element. EachRPR node in this ring is a zone gateway that represents a handoff zone,which is defined in terms of capacity, coverage, roaming topology andsecurity domain. Also shown is an additional RPR node 39 functioning asa data source or through which is connected a data source. As was thecase for the more general embodiment of FIG. 5, the inter-zone handoffcontroller 10 in some embodiments can function as an inter-zone gatewayfor traffic.

In this ring-tree handoff architecture, at the top level, the inter-zonehandoff controller uses a SOHO approach to multicast the data flows toall potential targeting zone-based handoff sub-controllers. Themulticasting can be implemented by utilizing RPR multicast capability.The choice of the targeting handoff zone(s) is made by network handoffintelligence. To reduce the cost in terms of traffic resourceutilization, the number of chosen target zones may be limited. Combinedwith wise handoff intelligence, SOHO starts sending the data flow to thetargeting zone before the mobile attaches to that target zone.

At each sub-tree level, an FBSS approach is used to conduct intra-zonehandoff procedure. For example, FBSS fast IP tunnel switching technologycan be applied in each zone to rapidly handoff from the serving basestation to the potential target base station.

In some embodiments, the handoff functions at the inter-zone handoffcontroller and/or the zone gateways have built-in algorithms todetermine a mobile station's mobility. They may communicate with eachother to decide when to start and when to stop SOHO operation. Thismight for example be based on a global paging control function, latestlocation update information of mobile, current zone ID, mobile directionand mobile speed. The analysis can be structured to minimize the numberof target zones, or at least to impose a maximum on the number of targetzones. Other algorithm parameters might include radio cell coverage,radio channel allocation, traffic pattern, bandwidth, QoS and networktraffic performance.

The described example uses IP tunnelling technologies to support FBSS ina wireless data access network. However, more generally, the approach isapplicable to all L3/L2 packet networks including IP-in-IP, Mac-in-Mac,MPLS label stack, RPR and R-bridge networks.

Control Architecture

An overall network-wise handoff control architecture can be implementedin three levels: a master handoff controller at the ring level,zone-handoff-controller at ring node level and handoff-agent at eachbase station level.

The master handoff controller communicates with thezone-handoff-controllers, which in turn, communicate with the basestation handoff agents, to collect mobile location information withpaging functions, and to co-ordinate global handoff functions. Thecommunication may be done via location enquiries periodically frommaster handoff controller, or via notifications reported byzone-handoff-controller and handoff agents.

The master handoff controller uses network intelligence to predict andto determine the potential handoff zones which the mobile is moving to,and to utilize RPR multicasting capability to deliver the data flows tothese target zones. The intelligent handoff algorithms make decisionsbased on the global paging control function, the latest location updateinformation of mobile, current zone ID, mobile direction and mobilespeed. Each RPR node is an ASN Gateway anchor switch which conductsintra-zone handoff procedure. This anchor switch pre-cache the receiveddata in the buffer (if it is a target zone), and distributes the dataflows to either the serving base station or the target base station viahandoff protocols/primitives. The intra-zone handoff procedure is FBSSapproach described in the following sections.

In another embodiment, the wireless access network includes relay nodes,for example, to either expand the coverage area of base stations, orenhance data rate ubiquity. In some cases, the relays are in fixedlocations such that the relationship between relays and base stations isfixed.

In other cases, relays can be provided in mobile locations, for exampleon trains. In such cases, the relationships between the relays and thebase stations are not fixed.

When the relays are fixed, in one embodiment, a third tier is added tothe hierarchical handoff approach. In this case, one can organize a basestation and associated relay station as a “virtual base station”. If amobile station moves from the coverage area of one relay of a given basestation to another relay of the same base station, it can be treated thesame as if the mobile station is moving from the coverage area of onevirtual base station to another virtual base station within the samenon-diversity handoff zone. The non-diversity handoff can then beperformed. For example, this might be performed analogously to the fastbase station switch between two virtual base station using a logicalinternal tunnel. This scenario is illustrated in FIG. 7A where a basestation 300 is shown in fixed relationship with two relays 302,304.Logically, base station 300 can be organized as two virtual basestations 305,307 respectively associated with relays 302, 304. At time_1(310, left side of drawing), a mobile station 306 is communicating withthe relay 302, and at time_2 (312, right side of drawing), the mobilestation is communicating with relay 304. In this case, the first virtualbase station 305 forwards traffic to the second virtual base station 307via internal tunnel 308 for some time, after which time the base station300 will forward traffic directly to the second relay with appropriatenewly assigned connectivity information. If the mobile station'smobility results in it moving to a different base station's coveragearea within the same FBSS zone, then FBSS handoff is performed asbefore. Finally, if the mobile station's mobility results in it movingto a different base station's coverage area that is not within the sameFBSS zone, then soft handoff is performed as before.

In another embodiment, the handoff between relays can be handled usinganother method, for example soft handoff.

When the relays are mobile, typically the mobile station and the relaymove together as a unit. An example of this scenario is depicted in FIG.7B. Shown is a first base station 330 and a second base station 332.Also shown is a relay 334 that is serving a mobile station 336, with therelay 334 and mobile station 336 moving more or less together. At time_1(340, left side of the figure) the relay 334 and mobile station 336 arebeing served by the first base station 330. At time_2 (342, right sideof the figure) the relay 334 and the base station 336 are being servedby the second base station 332. When the mobile station 336 plus relay334 move from the coverage area of one base station to the coverage areaof another base station, the handoff can be handled in the same way asif there was no relay. More specifically, if the new base station 332 isin the same FBSS zone as the previous base station 330, then a FBSShandoff is performed. If the new base station 332 is not in the sameFBSS zone as the previous base station 330, then a soft handoff isperformed.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

We claim:
 1. A method comprising: defining a plurality of non-diversityhandoff zones, each non-diversity handoff zone comprising a respectiveplurality of non-diversity-enabled base stations; to perform a handoffbetween a first base station and a second base station of said basestations: performing a non-diversity handoff to complete the handoff ifthe first base station and the second base station are in the samenon-diversity handoff zone; performing a diversity handoff to completethe handoff if the first base station and the second base station are indifferent non-diversity handoff zones.
 2. The method of claim 1 whereinperforming a non-diversity handoff comprises performing fast basestation selection.
 3. The method of claim 1 wherein performing anon-diversity handoff comprises performing fast base station switching.4. The method of claim 3 wherein performing fast base station switchingcomprises: a first base station acting as a serving base stationreceiving packets from a data source destined for the mobile station;the first base station transmitting packets to the mobile station; toimplement the fast base station switch to the second base station, thefirst base station forwarding to the second base station all packetsthat have not been transmitted to the mobile station or that have notbeen acknowledged by the mobile station; the second base stationreceiving the packets from the first base station; the second basestation transmitting packets received from the first base station to themobile station; later, the second base station receiving packets fromthe data source destined for the mobile station such that the secondbase station acts as a serving base station.
 5. The method of claim 4further comprising: establishing a tunnel between the first base stationand the second base station for forwarding packets between the firstbase station and the second base station.
 6. The method of claim 3further comprising: at the first base station: a) during non-handoffoperation, receiving the packets on an ingress port and queuing them inan ingress queue; b) during non-handoff operation, de-queuing packetsfrom the ingress queue and transmitting them over an air interface; c)during handoff, de-queuing packets from the queue and re-queuing them inan egress queue; d) during handoff, de-queuing packets from the egressqueue and sending them to the second base station on an egress handoffport; at the second base station: e) during handoff, receiving thepackets on an ingress handoff port and queuing them in an ingress queue;f) during handoff, de-queuing packets from the ingress queue andtransmitting them over an air interface.
 7. The method of claim 1further comprising: defining a plurality of virtual base stations eachcomprising a relay and a base station served by the relay; wherein forthe purpose of non-diversity handoff zones, each virtual base station istreated as a non-diversity-enabled base station.
 8. The method of claim1 further comprising: providing service to at least one mobile stationwith a mobile relay, the mobile relay and served mobile stationcomprising a mobile relay and mobile station pair; to perform a handoffof a mobile relay and mobile station pair between a first base stationand a second base station of said base stations: performing anon-diversity handoff to complete the handoff if the first base stationand the second base station are in the same non-diversity handoff zone;performing a diversity handoff to complete the handoff if the first basestation and the second base station are in different non-diversityhandoff zones.
 9. A system comprising: a plurality of base stationsorganized into non-diversity handoff zones; an inter-zone handoffcontroller; the system being adapted to perform handoffs between a firstof the base stations and a second of the base stations by: performing anon-diversity handoff to complete the handoff if the first base stationand the second base station are in the same non-diversity handoff zone;performing a diversity handoff under control of the inter-zone handoffcontroller to complete the handoff if the first base station and thesecond base station are in different non-diversity handoff zones. 10.The system of claim 9 adapted to perform a non-diversity handoff byperforming fast base station selection.
 11. The system of claim 9adapted to perform a non-diversity handoff by performing fast basestation switching.
 12. The system of claim 11 adapted to perform fastbase station switching by: a first base station acting as a serving basestation receiving packets from a data source destined for the mobilestation; the first base station transmitting packets to the mobilestation; to implement the fast base station switch to the second basestation, the first base station forwarding to the second base stationall packets that have not been transmitted to the mobile station or thathave not been acknowledged by the mobile station; the second basestation receiving the packets from the first base station; the secondbase station transmitting packets received from the first base stationto the mobile station; later, the second base station receiving packetsfrom the data source destined for the mobile station such that thesecond base station acts as a serving base station.
 13. The system ofclaim 9 further comprising a network hierarchical handoff controlarchitecture comprising said inter-zone handoff controller at inter-zonelevel, zone-handoff-controllers at intra-zone level and handoff-agentsat each base station.
 14. The system of claim 9 adapted to establish atunnel between the first base station and the second base station forforwarding packets between the first base station and the second basestation.
 15. The system of claim 9 wherein: the first base station isadapted to: a) during non-handoff operation, receiving the packets on aningress port and queuing them in an ingress queue; b) during non-handoffoperation, de-queuing packets from the ingress queue and transmittingthem over an air interface; c) during handoff, de-queuing packets fromthe ingress queue and re-queuing them in an egress queue; d) duringhandoff, de-queuing packets from the egress queue and sending them tothe second base station on an egress handoff port; the second basestation is adapted to: e) during handoff, receiving the packets on aningress handoff port and queuing them in an ingress queue; f) duringhandoff, de-queuing packets from the ingress queue and transmitting themover an air interface.
 16. A base station comprising: at least one inputport for receiving packets destined for mobile stations; an output portfor outputting packets on a tunnel towards another base station in acommon non-diversity handoff zone; physical layer hardware; a packetdispatcher adapted to transmit received packets for a given mobilestation to the given mobile station via the physical layer hardwarewhile the given mobile station is attached to the base station, suchthat the packet dispatcher continues to transmit received packets for agiven mobile station to the given mobile station during diversityhandoff to another base station in a different non-diversity handoffzone, and to send the packets towards the output port during a fast basestation switch handoff to the another base station in the commonnon-diversity handoff zone.